Dio Throws Exception on DELETE Request with 204 Response

[HHLiftBridge]

Package

dio

Version

5.5.0

Operating-System

Web

Adapter

Default Dio

Output of flutter doctor -v

[√] Flutter (Channel stable, 3.19.6, on Microsoft Windows [Version 10.0.22631.3880], locale en-US)
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    • Dart version 3.3.4
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    • Java version OpenJDK Runtime Environment (build 17.0.6+0-b2043.56-10027231)
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    • Android Studio at C:\Program Files\Android\Android Studio
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    • Edge (web)        • edge    • web-javascript • Microsoft Edge 127.0.2651.86

[√] Network resources
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Dart Version

3.3.4

Steps to Reproduce

Create a flutter application with dio as a dependency.

Send a DELETE request to an endpoint which returns a 204 "No Content" http status code.

Expected Result

The request goes through without throwing an exception.

Actual Result

The request throws a DioException with the message "SyntaxError: Unexpected end of JSON input".

[HHLiftBridge]

Please let me know if there's any more info I can add. Judging by the error message it seems that Dio is attempting to parse the body of the response, but since the response body is null, it throws this error.

The issue does not occur in 5.4.3, so I have downgraded the version for now.

Only tested with DELETE requests, I am not sure if other HTTP requests are affected.

Tested only in flutter web, I am not sure if other platforms are affected.

[kuhnroyal]

Please add sample code that shows how you call the delete endpoint. Make sure to use the correct generic response type .

[HHLiftBridge]

Here's the basic implementation of my HttpProvider class. For brevity, some methods like sendGet and sendPost are removed. I also cut out irrelevant details (such as a try-catch around the _dio.delete() method to throw my own error), but I checked and the "FormatException: SyntaxError: Unexpected end of JSON input" error still occurs with the code below.

class HttpProvider {
  HttpProvider({this.token}) {
    _dio = Dio(BaseOptions(connectTimeout: const Duration(seconds: 6000)));
    _dio.options.baseUrl = 'https://redacted'
  }
  String? token;

  Future<Options> _getOptions() async {
    Map<String, dynamic> headers = {
      'Strict-Transport-Security': 'max-age=63072000; includeSubDomains; preload',
    };
    if (token != null) {
      headers['Authorization'] = "TOKEN ${token!}";
    }
    return Options(headers: headers);
  }

  Future<Response<dynamic>> sendDelete(String url, [data, String? token]) {
    return _dio.delete(
      url,
      data: data,
      options: await _getOptions(token),
    );
  }

Request body:

{"ids":[1536]}

Response headers:

HTTP/1.1 204 No Content
Server: nginx
Date: Mon, 12 Aug 2024 12:31:47 GMT
Content-Type: application/json
Content-Length: 352
Connection: keep-alive
Vary: Accept, Authorization, Cookie, Origin
Allow: PATCH, DELETE, OPTIONS
Cache-Control: no-cache, no-store, must-revalidate
X-Frame-Options: DENY
X-Content-Type-Options: nosniff
Referrer-Policy: same-origin
Cross-Origin-Opener-Policy: same-origin
Access-Control-Allow-Origin: *
Access-Control-Allow-Methods: DELETE
Access-Control-Allow-Headers: X-Device-UID,Strict-Transport-Security,Authorization,Content-Type
Access-Control-Max-Age: 1728000

[knaeckeKami]

It seems that this might be an issue with the latest transformer from #2239

You set ResponseType.json, and

The server sets

Content-Type: application/json
Content-Length: 352

so the transformer expects JSON content.

This is a violation of the HTTP Spec
https://www.rfc-editor.org/rfc/rfc7230

A server MUST NOT send a Content-Length header field in any response
with a status code of 1xx (Informational) or 204 (No Content).

But the transformer still probably should be adapted to handle this more gracefully.

For now, you can work around this by setting ResponseType to .bytes